1. Field of the Invention
The present invention generally relates to a ball joint, and more particularly to a ball joint which exhibits excellent performance, accommodating variations in dimension of individual components constituting such a ball joint or variations in load applied thereto during assembly thereof.
2. Description of the Prior Art
A ball joint for use in a steering linkage, suspension or the like of an automobile includes in general a socket and ball stud. The ball stud includes a ball portion received in a socket hole of the socket for pivotal movement therein by means of a bearing intervening between the ball and the socket.
Such a bearing is formed from a synthetic resin material having a high wear resistance, representing low resiliency. An outer configuration of the bearing is designed to be identical to an inner configuration of the socket hole so as to permit the bearing to be received within the socket hole without any significant clearance therebetween. Accordingly, the bearing may produce a significant amount of variation in repulsive, resilient force, even if dimensional error of components constituting the ball joint is small.
Accordingly, and if dimensional accuracy of each component is decreased, a bearing, when assembled, will present significantly fluctuated repulsive, resilient force and thus constant operational torque of the ball stud could not be obtained. When the bearing is significantly worn, a substantial amount of clearance will be produced between the ball portion of the stud and the bearing, so that appropriate operational torque of the ball stud could not be maintained, thus adversely affecting performance of the joint.
Japanese Utility Model Public Disclosure No. 64-39922 and Japanese Utility Model Publication No. 63-17855, for example, disclose ball joints in an effort to eliminate the above problems experienced in the prior art.
The ball joint disclosed in Japanese Utility Model Public Disclosure No. 64-39922 includes a bearing formed in the outer surface thereof with protrusions and recesses adjacent thereto. When the bearing is installed in a socket hole, the above protrusions are urged against the wall defining the socket hole and are displaced into the recesses, so as to reduce variation in resilient, repulsive forces of the bearing. This ball joint, however, does not provide sufficient resilient, repulsive force due to the large amount of deformation of the protrusions. Further, it appears that durability of such a ball joint would be insufficient, since resilient, repulsive force will be decreased due to "creep" phenomenon of the protrusions. Furthermore, such a ball joint would cause significant variations in resilient, repulsive forces depending upon variation in deformation of the protrusions.
A ball joint disclosed in Japanese Utility Model Publication No. 63-17855 includes a socket hole having recesses in its wall at an inclined surface between cylindrical surface and bottom surface. Thus, this ball joint is designed to permit the ball stud to generate a stable operational torque, owing to the inclined surface of the bearing positioned above the depressions which generate a bending repulsive force. This joint however requires complicated manufacturing process in order to form recesses in the inclined surface of the socket hole. It takes a great deal of time to form the depressions by machining. When it is intended to form such depressions in a molding die during molding process, the life of the molding die will be shortened, since such die should have edge portions. In any case, forming the depressions in the inclined surface of the socket hole would increase manufacturing costs significantly.